Abstract
BACKGROUND
We conducted a phase I study to determine the maximum tolerated dose of bendamustine when given in combination with clofarabine, etoposide, and dexamethasone daily for 5 days in children and adolescents with relapsed or refractory hematologic malignancies.
METHODS
Patients younger than 22-year-old with second or greater relapsed or refractory acute leukemia or lymphoma following 2 or more prior regimens were eligible. Using the rolling 6 design, participants received escalating doses of bendamustine (30, 40, or 60 mg/m2/day) in combination with clofarabine (40 mg/m2), etoposide (100 mg/m2), and dexamethasone (8 mg/m2) daily for 5 days. Optional pharmacokinetic studies were performed in cycle 1 on day 1 and day 5.
RESULTS
Sixteen patients were enrolled. Six patients were treated on dose level 30, six on dose level 40, and four on dose level 60 mg/m2/day. The dose limiting toxicity was prolonged myelosuppression. The combination was otherwise well tolerated. The recommended dose of bendamustine in this combination is 30 mg/m2 per day for 5 days. Ten responses were observed after one cycle: 6 complete remissions, 1 durable minimal residual disease-negative complete remission without platelet recovery in a patient with Early T-cell precursor leukemia, and 3 partial remissions. Six patients proceeded to transplant. The event-free survival was 40.6% (95% CI, 17.5–63.7) at 1 year and 33.9% (95% CI, 11.9–55.9) at 3 years.
CONCLUSION
Bendamustine is well tolerated in combination with clofarabine, etoposide, and dexamethasone. The combination administered over 5 days is effective in multiple relapsed and refractory hematologic malignancies. This trial is registered with ClinicalTrials.gov (NCT01900509).
Keywords: Pediatric, Leukemia, Lymphoma, Relapse
LAY SUMMARY
Improvement in existing chemotherapy regimen is still needed for patients who relapse following targeted therapies and immunotherapies, and in those who are not eligible, or have no access to such therapies. A regimen combining cyclophosphamide, clofarabine, and etoposide has been used in relapsed and refractory pediatric patients with hematologic malignancies. In this study we show that substituting bendamustine for cyclophosphamide in combination with clofarabine and etoposide is safe and effective.
PRECIS
Bendamustine can safely be administered daily over five days in combination with clofarabine, etoposide, and dexamethasone. MRD-negative complete remissions were achieved in 70% of pediatric patients with relapsed or refractory B-ALL.
INTRODUCTION
The combination of cyclophosphamide, clofarabine, and etoposide is often used in the treatment of children and adolescents with relapsed hematologic malignancies. While effective, this 3 drug combination has been associated with increased risks of prolonged myelosuppression, severe infections, and hepatic toxicity.1–3 Many patients with relapsed hematologic malignancies have prior exposure to cyclophosphamide; moreover, most responders would receive additional cyclophosphamide as part of their conditioning regimen as they proceed to transplant. We conducted a phase I trial to evaluate the safety and efficacy of a regimen substituting cyclophosphamide with bendamustine in combination with clofarabine, etoposide, and dexamethasone.
DNA damage induced by bendamustine, an alkylating agent with a benzimidazole ring giving it anti-metabolite properties,4 is more durable and extensive than that caused by other alkylating agents such as cyclophosphamide and chlorambucil.5 Bendamustine also shows incomplete cross resistance with other alkylators.6 It was approved for use in the United States in 2008 as therapy for chronic lymphocytic leukemia,7 and its indications were later expanded to include indolent B cell non-Hodgkin lymphoma that is refractory to rituximab containing regimens.8–12 Bendamustine has also demonstrated activity against Hodgkin lymphoma,13–16 and encouraging responses have been reported in patients with T-cell neoplasms.17 Bendamustine is often given in combination with other antineoplastic agents on days 1 and 2 of 21- or 28-day cycles at doses ranging between 90 and 120 mg/m2 per dose. Another schedule that has been tested is bendamustine at 60 mg/m2 daily for 5 days every 4–6 weeks in patients with pre-treated low grade non-Hodgkin lymphoma with a response rate of 76%.18
In this study, we evaluated the maximum tolerated dose of bendamustine when administered in combination with clofarabine, etoposide, and dexamethasone over a 5-day cycle in pediatric patients with second or greater relapsed or refractory acute leukemia or lymphoma following 2 or more prior regimens.
PATIENTS AND METHODS
Participants
Patients with acute lymphoblastic leukemia (ALL), acute myelogenous leukemia (AML), biphenotypic leukemia, Hodgkin or Non-Hodgkin lymphoma, were eligible if they were younger than 22 years-old, had second or greater relapsed or refractory acute leukemia or lymphoma following 2 or more prior regimens, and had adequate organ function (ClinicalTrials.gov, number NCT01900509). A full listing of eligibility criteria is provided in Supplemental Material (online only). The protocol was approved by the institutional review board, and written informed consent was obtained from the parents, guardians or patients, with assent from the patients, as appropriate.
Study Design
The primary objective of the study was to establish the maximum tolerated dose (MTD) and the recommended phase 2 dose of bendamustine in combination with fixed doses of clofarabine, etoposide, and dexamethasone given daily for 5 days. The primary endpoints were to evaluate the safety profile of bendamustine in combination with clofarabine, etoposide, and dexamethasone, and to characterize the dose-limiting toxicity (DLT) of this regimen during cycle 1 of therapy. Secondary endpoints were to (1) estimate event-free survival at 4 months, (2) evaluate minimal residual disease (MRD) levels present at the end of each cycle of therapy in participants with leukemia, and (3) characterize the pharmacokinetic profile of bendamustine in the proposed regimen. Using the Rolling-6 design, 19 participants received escalating doses of bendamustine (30, 40, or 60 mg/m2/day) in combination with clofarabine (40 mg/m2/day), and etoposide (100 mg/m2/day). Dexamethasone (8 mg/m2/day) was administered daily for 5 days to prevent clofarabine associated systemic inflammatory response syndrome (SIRS).2 Each cycle lasted 21–28 days (or until count recovery). Participants received up to 2 cycles of therapy. The DLT observation period was defined as the duration of cycle 1 until blood count recovery (ANC ≥500) in the absence of marrow involvement by disease or myelosuppressive infection (Supplemental Material, online only). Toxicities were graded using the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE; version 4.0). Definition of dose limiting toxicity and disease evaluation criteria are provided in Supplemental Material.
Pharmacokinetics
Optional pharmacokinetic studies were done on days 1 and 5 of cycle 1 in consenting participants to assess for potential time-dependent changes in bendamustine clearance over the 5-day course in this combination regimen. Blood samples were collected at the following times from the start of the infusion: 50 min (10 min before the end of the 1-hour bendamustine infusion) and 1.5, 2, 3, 4 and 6 hours. Administration of clofarabine or etoposide was not started until the 2-hour blood sample was collected. Plasma concentrations of bendamustine were measured using an established and validated liquid chromatography mass spectrometry assay.20 The lower limit of quantitation for bendamustine was 0.5 ng/mL. The within-day and between-day precision (% coefficient of variation [CV]) values and accuracy values met standard assay validation criteria.
A linear 2-compartment model, with first-order elimination was used to model the data. The population pharmacokinetic and individual post-hoc estimates of bendamustine were determined using non-linear mixed effects modeling via Monolix (version 4.3.3, www.monolix.org) using the Stochastic Approximation Expectation-Maximization (SAEM) approach. Parameters estimated included: CL (L/hr/m2), the bendamustine clearance; V1/ (L/m2), the volume of bendamustine; Q (L/hr/m2), the intercompartmental clearance; V2 (L/m2), the volume of the peripheral compartment. The individual model parameters for each patient were used to simulate the plasma concentration-time profile, from which the area under the concentration curve (AUC) zero to 24 hours, maximum concentration (Cmax), and the time to maximum concentration (Tmax) were calculated for each pharmacokinetic study (day 1 and 5). The inter-individual and inter-occasion variability of the parameters was assumed to be log normally distributed. A proportional residual error model was used with assumed normal distribution of the residuals. Additional methods are provided in Supplemental Material.
Statistical Analysis
Any participant who experienced DLT at any time during cycle 1 of protocol therapy was considered evaluable for toxicity. The Rolling-6 design19 was used for the conduct of this study. Relapse, second malignancies, death due to any reason, and failure to achieve complete remission were considered as failures. Event-free survival (EFS) time was calculated from the on-therapy date to any kind of failure or to last contact date for participants who were alive without any failure at the last contact date. The time to EFS was set to 0 for participants who failed to achieve complete remission. Kaplan-Meier estimates of the EFS and overall survival (OS) functions were computed, along with estimates of standard errors by the method of Peto. 21 EFS and OS rates at 4 months, 6 months, 1 year and 3 years were estimated with 95% confidence intervals. MRD was obtained by flow cytometry at the end of each cycle of therapy in patients with ALL and was considered positive if the level was ≥0.01%. The prevalence of MRD at the end of each cycle was defined as the proportion of MRD positive results. These proportions were evaluated with point and interval estimates. The pharmacokinetic covariates age, body surface area, weight, and study day were evaluated to determine their significance in explaining pharmacokinetic variability. These covariates were considered significant in a univariate analysis if their addition to the model reduced the objective function value (OFV) at least 3.84 units (p < 0.05, based on the chi-square test for the difference in the −2 log-likelihood between 2 hierarchical models that differ by 1 degree of freedom), and the covariate term was significantly different than zero (p < 0.05, t-test).
RESULTS
Patient Characteristics
Sixteen patients (12 males and 4 females) with a median age of 11 years (range 5 to 17 years) were enrolled between October 2013 and March 2016: 10 patients with B-cell acute lymphoblastic leukemia (B-ALL), 1 with early T-cell precursor (ETP) leukemia, 1 with gamma delta T-cell ALL, 2 with Hodgkin lymphoma, and 2 with T-cell lymphoblastic lymphoma (Table 1). Participants had received a median of 3 prior regimens (range 2 to 8). Twelve patients (75%) were refractory to the last regimen they received, accounting for the relatively low number of patients with prior transplant (19%).
Table 1.
Patients Characteristics and Treatment Outcome
| Case | Age (yrs) | Gender | Diagnosis | # Prior Reg | Prior BMT | Dose Level mg/m2/d | DLT | # Cycles | Response to Cycle 1 | BMT | Status |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 6 | F | T-cell NHL/rR1 | 6 | No | 30 | No | 1 | SD | NA | Died of PD |
| 2 | 16 | M | T-cell NHL/rR1 | 3 | No | 30 | No | 1 | SD | NA | Died of PD |
| 3 | 10 | M | B-ALL/rR3 | 8 | No | 30 | No | 1 | SD | NA | Died of PD |
| 4 | 9 | F | B-ALL/R3 | 4 | Yes | 30 | Yes | 1 | CR (MRD <0.01%) | Yes | ALIVE in CR |
| 5 | 10 | M | Gamma-Delta/r | 2 | No | 30 | No | 1 | PD | NA | Died of PD |
| 6 | 17 | M | B-ALL/R2 | 2 | No | 30 | No | 2 | CR (MRD 0.124%) | Yes | ALIVE in CCR |
| 7 | 4 | F | B-ALL/rR2 | 3 | No | 40 | No | 1 | CR (MRD <0.01%) | Yes | ALIVE in CCR |
| 8 | 17 | M | B-ALL/R2 | 2 | No | 40 | No | 2 | CR (MRD <0.01%) | Yes | Died of BMT complications |
| 9 | 11 | M | B-ALL/rR1 | 2 | No | 40 | No | 1 | SD | NA | Died of PD post DOT1L |
| 10 | 14 | M | Hodgkin/rR1 | 3 | No | 40 | No | 2 | PR | (Yes) | Died of PD |
| 11 | 15 | M | B- ALL/rR1 | 3 | No | 40 | Yes | 1 | CR (MRD <0.01%) | No | Lost to follow up |
| 12 | 14 | F | Hodgkin/rR2 | 3 | No | 40 | Yes | 1 | PR | (Yes) | Alive |
| 13 | 9 | M | B-ALL/rR1 | 2 | No | 60 | No | 2 | CR (MRD <0.01%) | Yes | Alive in CCR |
| 14 | 11 | M | B-ALL/R2 | 2 | No | 60 | No | 2 | PR | Yes | Died of BMT complications |
| 15 | 12 | M | ETP/rR2 | 5 | Yes x 2 | 60 | Yes | 1 | Cri (MRD <0.01%) | No | Died of PD |
| 16 | 5 | M | B-ALL/rR2 | 7 | Yes | 60 | Yes | 1 inc | NA | NA | Died of TLS SIRS |
R, Relapse; r, refractory; inc, incomplete; SD, stable disease; CR, complete remission; Cri, CR with incomplete count recovery; PD, Progressive disease; BMT, bone marrow transplant; (Yes), BMT received post additional salvage treatment; CCR, continuous complete remission; DLT, dose limiting toxicity; MRD; minimal residual disease; NA not applicable
Safety
Six patients were treated on dose level 1 (bendamustine 30 mg/m2), six on dose level 2 (bendamustine 40 mg/m2), and four on dose level 3 (bendamustine 60 mg/m2). All patients were evaluable for toxicity and 15 for response. Fifteen patients completed all chemotherapy planned for cycle 1. One patient enrolled at dose level 60 mg/m2 received only 3 days of chemotherapy because of severe tumor lysis syndrome (TLS) and SIRS complicating his course and leading to death on day 8 of the cycle. Another patient at dose level 60mg/m2 did not have platelet recovery by day 42, resulting in 2 patients experiencing DLT at dose level 60 mg/m2. In addition, two patients at dose level 40 mg/m2 and one patient at dose level 30 mg/m2 did not have count recovery by day 42 (Table 1 and Supplemental Table S1). The recommended dose of bendamustine in this combination is 30 mg/m2 daily over 5 days.
The most common treatment-related adverse event was febrile neutropenia observed in 88% of patients completing cycle 1 chemotherapy (Table 2). The overall documented infection rate was 37%. Three patients had positive blood cultures (Streptococus Viridans, Escheridia coli, and Coagulase Negative Staphylococcus), 2 patients had Clostridium difficile colitis, 1 patient had Herpes Simplex Virus mucositis, 1 patient had Rhizopus pneumonia, and 1 patient had Stenotrophomonas maltophilia and Rhizopus sinusitis. The electrolytes abnormalities observed were expected with the supportive care medications provided to the patients. No patient died from infectious complications.
Table 2.
Grade 3–5 adverse events
| Treatment Cycle | Adverse Event | Dose Level | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 30 mg/m2 × 5 days (6 patients) | 40 mg/m2 × 5 days (6 patients) | 60 mg/m2 × 5 days (4 patients) | ||||||||
| Grade | Grade | Grade | ||||||||
| 3 | 4 | 5 | 3 | 4 | 5 | 3 | 4 | 5 | ||
| n | n | n | n | n | n | n | n | n | ||
| Cycle 1 | Acute kidney injury | 1 | 1 | |||||||
| Alanine aminotransferase increased | 2 | 1 | ||||||||
| Aspartate aminotransferase increased | 1 | |||||||||
| Capillary leak syndrome | 1 | |||||||||
| Disseminated intravascular coagulation | 1 | |||||||||
| Enterocolitis infectious | 1 | 1 | ||||||||
| Febrile neutropenia | 6 | 6 | 2 | |||||||
| Hyperglycemia | 1 | 1 | ||||||||
| Hypernatremia | 1 | |||||||||
| Hypokalemia | 1 | 1 | 2 | 1 | 1 | 1 | ||||
| Hyponatremia | 1 | |||||||||
| Hypophosphatemia | 1 | 1 | 1 | |||||||
| Hypotension | 1 | 1 | ||||||||
| Hypoxia | 1 | 1 | ||||||||
| Infections and infestations - Other, specify | 1 | 1 | ||||||||
| Left ventricular systolic dysfunction | 1 | |||||||||
| Lipase increased | 1 | |||||||||
| Lung infection | 1 | |||||||||
| Mucosal infection | 1 | 1 | ||||||||
| Mucositis oral | 1 | |||||||||
| Pulmonary edema | 1 | |||||||||
| Pulmonary hypertension | 1 | |||||||||
| Respiratory failure | 1 | |||||||||
| Sepsis | 1 | |||||||||
| Sinusitis | 1 | |||||||||
| Tumor lysis syndrome | 1 | |||||||||
| Number of patients with maximal AE Grade observed | 5 | 1 | 5 | 1 | 3 | 1 | ||||
| Cycle 2 | Alanine aminotransferase increased | 1 | ||||||||
| Aspartate aminotransferase increased | 1 | 1 | ||||||||
| Catheter related infection | 1 | |||||||||
| Febrile neutropenia | 1 | 1 | ||||||||
| Hypokalemia | 1 | |||||||||
| Hypotension | 1 | |||||||||
| Neuralgia | 1 | |||||||||
| Sepsis | 1 | |||||||||
| Skin infection | 1 | |||||||||
| Number of patients with maximal AE Grade observed | 1 | 1 | 1 | |||||||
Efficacy
Responses were observed in 10 patients following 1 cycle of therapy: 6 complete remissions (CR; all B-ALL), 1 durable MRD-negative CR without platelet recovery in the patient with ETP-ALL, and 3 partial remissions (PR; 2 Hodgkin lymphoma, 1 B-ALL) (Table 1). MRD was <0.01% in 5 of 6 patients achieving CR. The sixth patient, who was in CR with MRD detectable at 0.124% after cycle 1, achieved MRD < 0.01% following cycle 2 (Supplemental Table S2). An additional patient with B-ALL who was in PR following cycle 1 achieved an MRD-negative CR following cycle 2. Six patients received HSCT after achieving CR, four remain in continuous CR and two died from transplant complications. One patient with B-ALL achieving CR returned to his home institution and was lost to follow up. The patient with ETP leukemia in relapse following five prior regimens and two bone marrow transplants achieved MRD-negative CR without platelet recovery. He refused a third transplant or additional therapy and remained in remission for five months. Two patients with Hodgkin lymphoma achieved PR, then were taken off treatment to receive other salvage therapy followed by transplant; one remains in remission, and the other died from progressive disease post-transplant. Overall, 10 patients died (6 from progressive disease, 2 from transplant related complications, 1 from SIRS and 1 from complications of subsequent salvage chemotherapy). Both EFS and OS were 40.6% (95% CI, 17.5%−63.7%) at 1 year and 33.9% (95% CI, 11.9%−55.9%) at 3 years (Table 3 and Supplemental Figure S1).
Table 3.
EFS and OS at 4 months, 6 months, 1 year, and 3 years
| OS ± SE (%) | EFS ± SE (%) | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Dose Level mg/m2 × 5 days | n | Month 4 | Month 6 | 1 Year | 3 Years | Month 4 | Month 6 | 1 Year | 3 Years |
| 30 | 6 | 33.3 (2.5–64.1) | 33.3 (2.5–64.1) | 33.3 (2.5–64.1) | 33.3 (2.5–64.1) | 33.3 (2.5–64.1) | 33.3 (2.5–64.1) | 33.3 (2.5–64.1) | 33.3 (2.5–64.1) |
| 40 | 6 | 60.0 (22.8–97.2) | 60.0 (22.8–97.2) | 60.0 (22.8–97.2) | 40.0 (4.9–75.1) | 60.0 (22.8–97.2) | 60.0 (22.8–97.2) | 60.0 (22.8–97.2) | 40.0 (4.9–75.1) |
| 60 | 4 | 75.0 (38.2–100) | 75.0 (38.2–100) | 25.0 (0.0–55.0) | 25.0 (0.0–55.0) | 75.0 (38.2–100) | 50.0 (10.0–90.0) | 25.0 (0.0–55.0) | 25.0 (0.0–55.0) |
| All Patients | 16 | 54.2 (30.3–78.1) | 54.2 (30.3–78.1) | 40.6 (17.5–63.7) | 33.9 (11.9–55.9) | 54.2 (30.3–78.1) | 47.4 (23.5–71.3) | 40.6 (17.5–63.7) | 33.9 (11.9–55.9) |
OS, overall survival; SE, standard error; EFS, event-free survival.
Five patients (31%) received a second cycle: one at dose level 30 mg/m2, two at dose level 40 mg/m2, and two at dose level 60 mg/m2 (Table 4). Two patients received a second full cycle of chemotherapy, and three received only 60% (3 of 5 days) as allowed by protocol for patients bridging to transplant. Table 4 shows day to count recovery in both cycles. No significant toxicities were noted in the second cycle (Table 2). Responses were maintained or improved in patients with B-ALL who received 2 cycles (Supplemental Table S2). A patient with Hodgkin lymphoma who received a full second cycle, maintained a PR achieved with first cycle.
Table 4.
Days to Count Recovery
| Case | Dose Level (mg/m2/day) | Cycle 1 % chemo | Day Count Recovery | Cycle 2 % chemo | Day Count Recovery |
|---|---|---|---|---|---|
| 1 | 30 | 100% | Day 25 | NA | NA |
| 2 | 30 | 100% | NA* | NA | NA |
| 3 | 30 | 100% | NA* | NA | NA |
| 4 | 30 | 100% | Day 50 | NA | NA |
| 5 | 30 | 100% | NA* | NA | NA |
| 6 | 30 | 100% | Day 40 | 60% (3 days) | Day 14 |
| 7 | 40 | 100% | Day 31 | NA | NA |
| 8 | 40 | 100% | Day 29 | 60% (3 days) | Day 31 |
| 9 | 40 | 100% | NA* | NA | NA |
| 10 | 40 | 100% | Day 33 | 100% | Off therapy Day43 prior to count recovery |
| 11 | 40 | 100% | Day 47 | NA | NA |
| 12 | 40 | 100% | Prolonged myelosuppression* | NA | NA |
| 13 | 60 | 100% | Day 29 | 60% (3 days) | Day 16 |
| 14 | 60 | 100% | Day 34 | 100% | Day 36 |
| 15 | 60 | 100% | No platelet recovery | NA | NA |
| 16 | 60 | 60% (3 doses) | NA (Expired on Day 8) | NA | NA |
Off therapy prior to Day 42 due to no response
Pharmacokinetics
Bendamustine pharmacokinetic studies were obtained in 16 patients. All patients had pharmacokinetics evaluated on both days 1 and 5, except for one patient in the 60 mg/m2 dose group who did not complete 5 days of therapy due to the development of SIRS. Population pharmacokinetic values are presented in Supplemental Table S3. There was no significant difference in the day 1 vs day 5 bendamustine clearance (p=0.3). The median (range) day 1 AUC values for the 30 mg/m2, 40 mg/m2 and 60 mg/m2 dose cohorts were 1749 (893, 4653), 2045 (1721, 3773), and 3655 (2537, 13223) µg/L*hr (Figure 1). Of note, the highest day 1 bendamustine AUC of 13223 µg/L*hr was observed in the patient in the 60 mg/m2 dose group who developed severe TLS and SIRS. The median AUC increased proportionally to the dose (Supplemental Table S4). None of the covariates considered had a statistically significant effect on the pharmacokinetics of bendamustine (p>0.05).
Figure 1.
Day 1 area under the bendamustine plasma concentration-time curve in patients receiving 30 mg/m2 (n=6), 40 mg/m2 (n=6) and 60 mg/m2 (n=4) bendamustine. The box indicates the 25th to 75th percentile, the red horizontal line shows the median, and the vertical bars indicate the range.
DISCUSSION
Prior and ongoing studies focus on bendamustine therapy in Hodgkin and Non-Hodgkin lymphoma, and in adult indolent hematologic malignancies. In a Phase 1/II trial in children and young adults, 27 patients with ALL and 16 patients with AML received single agent intravenous bendamustine on days 1 and 2 of each treatment cycle.22 In the phase I portion of that study, 5 patients received bendamustine 90 mg/m2 and 6 received bendamustine 120 mg/m2. No DLTs were observed with either dose. At 120 mg/m2, plasma concentrations were within the therapeutic range for adults, with Cmax ranging from 3494 to 9137 ng/mL, AUC0–24 from 5322 to 14,039 ng h/mL, and AUC0-t from 5322 to 14,039 ng h/mL. An additional 32 patients received bendamustine at the recommended phase II dose of 120 mg/m2. Two patients with ALL treated at 90 mg/m2 achieved CR. Among patients who received bendamustine 120 mg/m2, 2 experienced PR and 7 had stable disease. No patients with AML responded. The most common adverse events were anemia, neutropenia, thrombocytopenia, pyrexia, nausea, vomiting, and diarrhea.22 While bendamustine demonstrated single agent activity against pediatric ALL in that study, the suboptimal response rate could be due to the 2 day single agent dose schedule which works better for slowly proliferative malignancies than for childhood acute leukemias. In preclinical studies, we explored anti-leukemic effects of bendamustine alone or in combination with clofarabine and etoposide. Across four ALL cell lines, bendamustine exhibited potent cytotoxicity in the micromolar concentration range which is achievable in patients. Interestingly, bendamustine also potentiated the activity of etoposide and/or clofarabine in a synergistic or additive fashion in vitro (Supplemental Table S5).
The prospective study reported here is the first to substitute bendamustine for cyclophosphamide in combination with clofarabine, etoposide, and dexamethasone for children with relapsed/refractory hematologic malignancies. In the 10 patients with B- ALL enrolled, 6 achieved MRD-negative CR following cycle 1, with one additional patient achieving MRD-negative CR following cycle 2 (i.e. composite MRD-negative CR rate with 2 cycles of 70 %). These results compare favorably with the 28% CR rate and 44% overall response rate reported in a phase 2 study of cyclophosphamide in combination with clofarabine and etoposide,2 and with the 39% CR rate (and 20% MRD-negative CR) reported in a pediatric phase 1/2 study of blinatumomab.23 The results are comparable to those reported with a bortezomib-based anthracycline containing regimen.24 Survival rates after chemotherapy salvage in patients with multiple relapses of ALL is historically dismal, with 5-year DFS reported as 27% after second CR and 15% after third CR.25 Therefore, we are encouraged with the durability of response in our cohort of patients. Due to small numbers, it was not possible to adequately evaluate responses in other pediatric hematologic malignancies. Bendamustine seems to be better tolerated than cyclophosphamide in this combination reported previously.2 The observed infectious complications were as expected in this patient population. No patient died secondary to infection, and we did not observe any hepatoxicity with this regimen. In comparison, 24% of patients treated with cyclophosphamide in combination with clofarabine and etoposide study died because of treatment-related adverse events associated with infection, hepatotoxicity, and/or multiorgan failure. Only 1 patient died from toxicity on the current study: a 5-year old patient with hyperleukocytosis who developed severe tumor lysis syndrome following day 1 of cycle 1 at dose level 3 (bendamustine 60 mg/m2). The day 1 bendamustine AUC observed in this patient of 13223 µg/L*hr was more than 3-fold higher than the median AUC for the other patients at this dose level and was within the range observed in adult and pediatric patients receiving bendamustine 120 mg/m2. 26 He received days 2 and 3 therapy after stabilization of tumor lysis, but became hypotensive and acidotic and had recurrence of tumor lysis syndrome after the third dose, and died from severe SIRS. Of note this patient had received 7 prior regimens and a bone marrow transplant. His relapse was refractory to 4 salvage treatments including CART-cell therapy and moxetumomab. Modification of the dose schedule, close monitoring, and preventive measures for patients with high tumor burden and multiple salvage regimens including transplant and immunotherapy may be warranted.
We obtained pharmacokinetic studies to assess for potential time-dependent changes in bendamustine clearance over the 5-day course in this combination regimen, because most previous pharmacokinetic studies of bendamustine have been conducted in adult patients with dose schedules of 90–120 mg/m2/day for 2 days. With intravenous administration over 30–60 minutes, peak bendamustine serum concentration is typically achieved by the end of the infusion.26 The elimination of bendamustine is triphasic with a rapid distribution phase, intermediate phase and slow terminal phase.27 A pediatric single-agent, single-dose study was completed which demonstrated that the overall pharmacokinetic profile of bendamustine was comparable to that in adults. Exposures reflective of the therapeutic range in adults were attained in children following administration of bendamustine at 120 mg/m2 infused over 60 minutes. The current study is the first combining bendamustine with clofarabine and etoposide over a five-day cycle. The population estimated clearance observed in our pediatric cohort receiving 30 to 60 mg/m2 (16.3 L/hr/m2 (IIV: 38 CV%)) was similar to that in a pediatric population receiving 90 or 120 mg/m2 doses (14.2 L/hr/m2 (IIV: 32 CV%)).27 The day 5 bendamustine clearance did not differ significantly from the day 1 clearance, indicating no evidence that the combination regimen altered bendamustine clearance.
In conclusion, bendamustine is well tolerated when administered over 5 days in combination with clofarabine, etoposide, and dexamethasone. This regimen has promising efficacy in relapsed and refractory hematologic malignancies, with the highest response rates observed in patients with B-ALL. The observed MRD-negative CR rate of 70% in patients with B-ALL is comparable to that observed with novel immunotherapeutic approaches. This regimen is a reasonable option for patients who are ineligible for, or who have relapsed after immunotherapy. Dose reductions on the first day of therapy are warranted in patients at risk of tumor lysis syndrome to avoid severe SIRS.
Supplementary Material
ACKNOWLEGMENTS
The authors thank the study participants and their families for their contributions to this study, and Jeana Cromer for project management.
SUPPORT
Partial funding was provided by TEVA Pharmaceuticals (as well as the investigational drug), the National Cancer Institute [St. Jude Cancer Center Support (CORE) under Grant P30 CA21765], and the American Lebanese Syrian Associated Charities (ALSAC). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
Footnotes
The authors have no conflict of interest
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